Re: [Xen-devel] [PATCH v2 2/2] VT-d: Fix vt-d flush timeout issue.

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 11.12.15 at 09:01, <quan.xu@xxxxxxxxx> wrote:
> On 11.12.2015 at 3:28pm, <Tian, Kevin> wrote:
>> > From: Xu, Quan
>> > Sent: Thursday, December 10, 2015 5:33 PM
>> >
>> > If IOTLB/Context/IETC flush is timeout, we should think all devices
>> > under this IOMMU cannot function correctly.
>> > So for each device under this IOMMU we'll mark it as unassignable and
>> > kill the domain owning the device.
>> >
>> > If Device-TLB flush is timeout, we'll mark the target ATS device as
>> > unassignable and kill the domain owning this device.
>> >
>> > If impacted domain is hardware domain, just throw out a warning. It's
>> > an open here whether we want to kill hardware domain (or directly
>> > panic hypervisor). Comments are welcomed.
>> >
>> > Device marked as unassignable will be disallowed to be further
>> > assigned to any domain.
>> >
>> > Signed-off-by: Quan Xu <quan.xu@xxxxxxxxx>
>> > ---
>> [...]
>> > diff --git a/xen/drivers/passthrough/vtd/iommu.h
>> > b/xen/drivers/passthrough/vtd/iommu.h
>> > index ac71ed1..c3beaa6 100644
>> > --- a/xen/drivers/passthrough/vtd/iommu.h
>> > +++ b/xen/drivers/passthrough/vtd/iommu.h
>> > @@ -452,6 +452,11 @@ struct qinval_entry {
>> >
>> >  #define RESERVED_VAL        0
>> >
>> > +#define INVALID_DID    ((u16)~0)
>> > +#define INVALID_SEG    ((u16)~0)
>> > +#define INVALID_BUS    ((u8)~0)
>> > +#define INVALID_DEVFN  ((u8)~0)
>> > +
>> 
>> Are those invalid values defined by specification? 
>  This is not defined by specification.
> 
>>Or if they are software
>> defined, does related mgmt. code guarantee that they won't be allocated?
>> 
> 
> As similar as the other Xen code, it defined invalid value with "~0". Such 
> as:
>           $#define INVALID_MFN (~0UL)
>           $#define INVALID_GFN (~0UL)
>           .etc
> 
> Code can't not guarantee that won't be allocated, but it can guarantee it 
> will not be used when it is INVALID_*.
> Any idea, how to indicate that the value is invalid?

Some other means is needed (be creative). Comparing with
INVALID_{MFN,GFN} is bogus, since frame numbers truly can't
reach this big a value (there being just 52 bits in physical
addresses, i.e. 40 bits in a frame number).

Jan


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